The present invention generally relates to vehicle test fixtures which simulate vibrational effects of road conditions and, more specifically, to an improved dynamic test fixture suitable for testing a vehicle exhaust system with twelve degrees of freedom (DOF).
Generally, a vehicle exhaust system must perform several demanding and diverse requirements, i.e., attenuating engine noise while porting and reducing emission levels of engine exhaust gas to the atmosphere. In addition, legislative action in combination with typical market driven design concerns have made the need for durable exhaust systems greater than ever before.
Thus, the need for determining exhaust system durability in a cost effective manner has generated demand for a system capable of verifying complete system performance prior to integration with a vehicle. Due to reduced product cycle time, physical testing of system level hardware and durability has been used to validate computer aided engineering (CAE) analysis. However, the analytical methods of determining durability to date have not proven completely accurate. Thus, physical test fixtures are typically used in an attempt to simulate actual road conditions for measuring system durability.
However, the problem with using physical test fixtures is that the demonstrated reliability and failure mode/mechanisms of the test results is directly related to the realism with which the input control signals/boundary conditions simulate actual road conditions. While the structural materials of the exhaust system have generally predictable responses, other factors such as exhaust hanger isolations are nonlinear or not well defined but will greatly influence the exhaust system dynamic loads, accelerations, and displacements. In addition, to date, available test fixtures have not been capable of supporting control signals for testing an exhaust system up to 12 DOF. With a higher DOF, test conditions and control signals can be made more realistic and reliable. As a result, a need exists for an improved test fixture capable of providing up to 12 DOF to work in conjunction with an arrangement for defining control signals and boundary conditions of 12 DOF for application to the test fixture.
It is, therefore, an object of the present invention to provide a test fixture for testing a vehicle exhaust system that is capable of up to at least 12 DOFs of motion.
In accordance with this and other objects, the present invention provides an exhaust system test fixture capable of at least twelve degrees of freedom including a first test fixture table arranged to mechanically support a vehicle engine and powertrain simulation apparatus, and a first set of actuators arranged to control motion of the first test fixture table in six degrees of freedom. A second test fixture table is arranged to mechanically support a vehicle exhaust system while connected to the engine and powertrain simulation apparatus supported on the first test fixture table, and a second set of actuators are arranged to control motion of the second test fixture table in six degrees of freedom. A controller is connected to the first and second set of actuators for generating actuator control signals to control movement of both test fixture tables based on determined boundary conditions.
In accordance with one aspect of the present invention, determination of the boundary conditions includes determining the number of degrees of freedom (DOF) from 1 to 6 needed to control each of the engine/powertrain and chassis relative to the tested exhaust system. The actuator control signals are determined based on the determined boundary conditions in combination with a first control model arranged to control engine/powertrain motion relative to a test floor, and a second control model arranged to control powertrain motion relative to the first test table if the test fixture is to be operated in a powertrain frame attached mode.
In further accordance with the present invention, an exhaust system test fixture capable of at least twelve degrees of freedom is provided having a test fixture table arranged to mechanically support a vehicle engine and powertrain simulation apparatus, a first set of actuators arranged to control motion of the test fixture table in six degrees of freedom, and a support fixture directly connected to one of the engine and exhaust system. A second set of actuators are connected to the support fixture to control motion in at least six degrees of freedom. A controller is connected to the first and second set of actuators for generating actuator control signals to control movement of the test fixture table and support fixture based on determined boundary conditions. In accordance with one aspect, a single table test fixture arrangement is provided such that the support fixture is connected to the engine, and comprises a frame positioned on top of the test fixture table and connected to the engine via the second set of actuators. In accordance with another aspect, a direct attachment test fixture arrangement is provided such that the support fixture is connected to the exhaust system at each hanger point and is arranged to connect the second set of actuators to the exhaust system at the hanger points.
Thus, the present invention provides an exhaust system test fixture capable of imparting motion that will reproduce the dynamic behavior of the vehicle engine/powertrain during operation in conjunction with reproducing the dynamic behavior of the vehicle chassis during operation in the area where the exhaust system is attached to the vehicle chassis.
The above object and other objects, features and advantages of the present invention are more readily understood from a review of the attached drawings and the accompanying specification and claims.